title: Inner retinal oxygen delivery and metabolism under normoxia and hypoxia in rat.
abstract: OBJECTIVE
  Retinal hypoxia is a common pathological condition usually caused by ischemia that may result in alterations in oxidative energy metabolism. We report measurements of oxygen delivery by the retinal circulation (DO2_IR) and inner retinal oxygen metabolism (MO2_IR) under systemic normoxia and hypoxia in rat.
  
  
  METHODS
  Rats were ventilated with fractions of inspired oxygen (FiO2) to induce either normoxia (n = 10), moderate hypoxia (n = 14), or severe hypoxia (n = 10). Oxygen tension was measured in retinal vessels using phosphorescence lifetime imaging and converted to arterial (O2A) and venous (O2V) oxygen contents. Total retinal blood flow (F) was assessed by red-free and fluorescent microsphere imaging. DO2_IR and MO2_IR were calculated as the products of F and O2A, and F and the arteriovenous oxygen content difference (O2A-V), respectively.
  
  
  RESULTS
  Measurements of O2A, O2V, and O2A-V were significantly reduced with decreased FiO2 (P < 0.001). In response to reduced oxygen availability, F increased under moderate hypoxia (P < 0.001) but did not increase further under severe hypoxia (P = 0.5). DO2_IR was similar under normoxia and moderate hypoxia (P = 0.7), but significantly lower under severe hypoxia (P < 0.001). Likewise, MO2_IR under normoxia and moderate hypoxia was similar (P = 0.1), but significantly reduced under severe hypoxia (P ≤ 0.02).
  
  
  CONCLUSIONS
  DO2_IR and MO2_IR were maintained during moderate hypoxia, but reduced under severe hypoxia, indicating blood flow compensation became insufficient for the reduced oxygen availability. Future studies may aid our understanding of retinal metabolic function in ischemic conditions.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Wanek
authors.forename: Pang-Yu
authors.initials: PY
authors.lastname: Teng
authors.forename: Norman P
authors.initials: NP
authors.lastname: Blair
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Shahidi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004195:Disease Models, Animal; D000860:Hypoxia / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D012039:Regional Blood Flow / Q000502:physiology; D012160:Retina / Q000378:metabolism* / Q000502:physiology; D012171:Retinal Vessels / Q000378:metabolism
chemical_list: D010100:Oxygen
keywords: delivery; hypoxia; metabolism; oxygen; retina